1. Field of the Invention
The present invention relates to a system that measures untwisting tension in a draw-false twisting machine and manages troubles occurring in the draw-false twisting machine itself and the quality of draw-false twisted textured yarn based on the data for the measured untwisting tension.
2. Description of the Related Art
Draw-false twisting machines for draw-false twisting of synthetic fibers made of thermoplastic resins such as polyester, nylon, etc. are widely used for production of false twisted textured yarn, by passing fed incompletely drawn yarn (hereunder referred to simply as "feed yarn") through a heater and drawing it while twisting with a false twisting unit. The twisting unit is included to provide twisting by keeping the yarn to run while in contact with a rotating friction surface at a fixed angle, and as twisting systems for the twisting unit there are known spindle twisting systems, belt twisting systems, friction disk twisting systems, etc. In all of these twisting systems, the feed yarn being twisted by the twisting unit is set by heating with heating means during the twisting step, after which it is untwisted to give it a false twisted shape and textured into false twisted yarn.
Incidentally, in the draw-false twisting step, defects in the feed yarn such as broken filaments and fluff appear as unusual untwisting tension. Consequently, it has become conventional to perform quality management in draw-false twisting machines, by time sequence monitoring of the untwisting tension, such as by the technique described in Japanese Unexamined Patent Publication No. 7-138828.
It has also become a recent practice to detect and measure untwisting tension with a tension sensor, such as by the technique described in Japanese Unexamined Patent Publication No. 6-264318, and to grade the quality on the packages of wound draw-false twisted yarn based on those results. Another method is to also add tension control means for adjustment of the yarn delivery force and the twisting force in the false twisting unit so that the untwisting tension falls within the target management range.
However, after much diligent research on untwisting tension, the present inventors have confirmed that the untwisting tension level often varies by about .+-.5 g depending on the properties of the feed yarn. If such large tension variation is arisen, it is highly possible that the feed yarn will experience some sort of trouble in processing under conditions that are different from normal, in a step other than the draw-false twisting step.
Despite this, uniformly maintaining the untwisting tension level within a management range by tension control means such as disclosed in Japanese Unexamined Patent Publication No. 6-264318 can result in failure to notice production trouble hysteresis even if the feed yarn that is fed to the draw-false twisting step is sometimes prepared under conditions with some sort of trouble. In the worst case, feed yarn that has experienced trouble may be subjected directly to the false twisting step and sent to the market as a textured yarn package.
In light of the circumstances alluded to above, the present inventors have diligently analyzed the factors involved in the variation in untwisting stress during the false twisting step, and as a result have found that this variation is closely related to the filament properties of the feed yarn, such as denier unevenness and orientation unevenness. It was also found that the following serious problems are inherent in conventional real-time untwisting tension monitor systems which simply monitor the actual values of untwisting tension online with the passage of time.
Specifically, it was found that if the untwisting tension is simply measured with the passage of time and the tension level value is managed within a given range or the cycle of the varying tension and the size of its amplitude is managed, to judge the stability of the process, this is completely ineffectual for judging what sort of trouble the feed yarn has undergone during processing, and the step in which it has occurred.
For this reason, even when variation occurs in the untwisting tension during the draw-false twisting step, it is very difficult to judge what trouble has occurred at which stage of preparation of the yarn fed to the draw-false twisting step, or what sort of trouble has occurred at what location in the draw-false twisting machine itself, and in fact absolutely no attempt has been made to discover these factors based on the untwisting tension.
Thus, a great deal of effort and time is required to investigate the cause of trouble with textured yarn or a problem of the draw-false twisting machine itself during the draw-false twisting step. In addition, the measures taken for the yarn preparation after discovering the cause are often delayed by a few weeks, and even when trouble occurs with the false twisting machine itself the trouble in the draw-false twisting machine is sometimes not realized and the problematic state therefore continues for future draw-false twisting.
Moreover, the values for the monitored untwisting tension variation include variation which is completely unrelated to the properties of the feed yarn, such as noise by machine vibration of the draw-false twisting machine, and its influence can result in misinterpretation of the data.